Ultraviolet photodetectors are useful in medical, communications, and defense applications. The photodetectors can include single crystalline silicon, silicon carbide, or gallium nitride p-n junction photodiodes. When the p-n junction of a photodiode is illuminated by light, photons excite electrons, causing free electrons and holes to be generated. Due to the built-in electric field at the depletion region, the free electrons move toward the cathode and the holes move toward the anode, producing a photocurrent that can be measured.